This is Coop and Eli pretending to play “Teenage FBI” by Guided by Voices. Or, it could be “Monkey Wrench” by Foo Fighters. Coop got all Ray Davies on poor Eli and started bossing him around, telling Eli he wasn’t playing something right (I never did figure it out). But, Eli kept banging away happily.
I hope they keep doing this kind of stuff, but I also hope they learn how to play their intstruments better.